ADC interrupts , some doubts

[vinodstanur]

Actually what is ADC interrupts?(pic16f877a)
I had read that if ADIE is enabled, then after AD conversion, ADIF will be set..
Actually, what is the significance of ADC interrupt?
I just started to learn about interrupts ...and alreadygot some idea about timer interrupts and RB0 INT in PIC16F877A...
But now, actually am confused abt ADC interrupts...
1>whats the need of ADC interrupts?
2>Could any one give a good situation where the ADC interrupts are essential..

 

[wp100]

Hi,

When using the pic 16F ADC in a typical hobbyist circuit its quiet normal to set the ADC routine off and then test and wait for the GO/DONE bit to clear to say the ADC conversion has completed and the result placed in the ADRES register/s.

bsf ADCON0,GO ; start conversion
a2d_done:
btfss ADCON0,GO ; this bit will change to zero when the conversion is complete
goto a2d_done

If you are using a faster pic /clock speed and the ADC is a relativley slow conversion, then rather than having the main program loop waiting for the ADC result you can first enable the Ato D interrupt ADIE , then start the ADC conversion, when its complete the Ato D Interrupt Flag will be set so creating the jump to the ISR, where the result can be serviced and the ADIF reset etc.

 

[vinodstanur]

So, after setting ADGO=1 , then the PIC can do the ADC in background and at the same time, it can execute the next instruction after ADGO=1 .
Am I right?
And , what is the approximate time required for ADC in pic16f877a?

 

[wp100]

Hi,

Am I right?

Yes thats the idea, though its not a method I have actually used.

If you see the datasheet ADC section and the ADC Conversion details in the Electrical Specification section it indicates around 20 -40 us, but that of course depends on your ADC settings and clock speed - again its not something I have actually measured - in my own adc programming I just test and wait for the conversion.

 

[Tahmid]

It's around what wp100 stated, but the accuracy is greater if you use a greater time instead of the fastest, esp at high frequency inputs.

Hope this helps.
Tahmid.

 

[anj]

Hi... though its an old thread. but I am a newbie and I want to know that is it possible to store results after conversion using FSR and INDF by setting address values to FSR??
i have tried like this in 16f886 in mplab using hitech c universal compiler:

for(FSR=0XE0;FSR<0XEA;FSR=FSR+1)
{
GO=1;
while(GO==1);
INDF=ADRESL;
delay_ms(2);
}

i dont know weather this is valid or not?
i can post my works too if you need. please help.